Monday, April 20, 2009

Brief warmup.. then cooler with rain (or even snow!) possible by end of week

After a cool gloomy weekend, the weather will be getting a little brighter and warmer over the first half of this week. Clouds will give way to sunshine today which will allow temperatures to get to the 10 degree mark. Tuesday should be dry with sunshine mixing with some high cloud ahead of a weak disturbance moving through southern SK. On Wednesday a stronger storm system will track through the central Prairies bringing an increasing southerly flow over southern MB with temperatures climbing into the mid teens over the RRV, possibly hitting 20 degrees over SW MB. On Thursday, the storm system will drag a cold front through southern MB, bringing cooler air back into the province by the end of the week. This frontal zone will stall south of the US border late in the week through the weekend, with several impulses moving along the frontal zone that may threaten rain over the Red River valley Friday into the weekend. In fact, the air will be cold enough that rain may change to wet snow over higher elevations of SW MB. Cooler than normal weather is expected into next week.

16 comments:

Canadian GLB model keeps late week precipitation well south of Manitoba while GFS shows potential for significant rainfall along southern MB especially near the US border. This explains the sunny forecast from Environment Canada for the end of the week, while other forecasts are calling for the chance of rain by the end of the week. Ensembles are showing a chance of some precipitation over Winnipeg by Friday/Saturday time frame. Canadian GLB may indeed verify, but it's important to note the possibility of precipitation over our area, especially in light of the current flooding situation in the RRV.

We knew that 23 was out of reach for Winnipeg, but 11 may be a little on the cool side. In addition, I think it will be a lot cloudier than the sunny forecast right now, as there should be overrunning cloud ahead of a warm front moving through southern MB Wednesday along with a chance of showers especially through the Interlake. It appears models have slowed down the warm front, and we may get briefly in the warm sector Thursday morning before cooling down again.

Done properly, long range forecasts should not exhibit such extreme day to day variability. Using an ensemble average instead of a deterministic single-model solution would cut down on the day to day variability that often accompanies successive model runs. The ensembles will be more conservative and may not catch the extremes, however they will not be as "wrong" either, and will usually trend in the right direction as the day approaches.

Newest GFS takes late week precipitation mainly south of the border through the Dakotas.. missing much of southern MB, but still impacting the southern end of the Red River valley mainly south of GFK. Meanwhile, the Canadian GLB model has trended further north with rain and possibly wet snow along the US border Friday into Saturday. For now, stick with the ensembles showing main swath of precip along the US border and northern ND with pcpn chances falling off north of the TransCanada.

Temperaturewise, looks like below normal temperatures persisting through the end of April, which will make this our fifth month in a row below normal. Here's hoping for a pattern change for the next 6 months.

That was back in the record dry April of 1980.. just a trace of rain all month and the sunniest April ever recorded. That was followed by a very dry May that saw 11 days over 30 degrees.. including a 9 day stretch from May 19-27th where temperatures peaked at an amazing 37.0C on the 22nd. Ahhh.. those were the days..

Rob, give me a ray of hope please. The U.S. CPC 8-14 day forecast continues to show us below average temps. The trend of the past winter of colder than normal just doesn'r seem to show any sign of letting up. Should we consider oursleves on track to repeat last summer's cooler than normal suummer? Whatever happened to a warm spring?

Will it snow.. and if so how much will accumulate? Those are the important questions for tonite.Impressive surface temperature gradient as mentioned with cold front well to our south.

There is strong baroclinic region at midlevels over us. Difficult to guess how much frontogenesis is present without Q/F vector analysis. Also impossible to say if CSI is present. Would require model cross section of isentropic and momentum surfaces.

We will be under right entracne region of large 300 hPa jet streak. This is a favored area for upper divergence/ low level divergence.

There is often synergy between the direct thermal circulations from frontogenesis and right entrance regions enhancing upward motion. The problem is this case is the lack of isentropic lift and warm/moist advection.

Nose of LLJ is pointed towards Minnesota and N Ontario. With no convergence from the LLJ and a lack of warm moist advection and elevated instability... potential for heavy precip is not there.

What lift we do have may interact with possible symmetric instability present to produce localized banding of snow.

All in all 5-10 mm of water equivalent in the form of wet snow south and east of a Melita to Winnipeg to Pinawa line looks reasonable. Snow will not stick at first due to warm ground. Snow rates will also not be intense except possibly in localized bands. Therefore maybe 2-3 cm of slushy accumulations is possible.

It will definitely be cold enough for snow overnight into Friday, but as Daniel mentioned, best bet for any snowfall should be south of Winnipeg.. with minimal amounts. Note that models continue to hint at a possible snowfall over Eastern SK and western MB early next week with a slow moving system along the MB/SK border.

Not nice to be even talking about this stuff this late.. but note that a year ago we had 2 snowstorms near us (one on the 24th and one on the 26th) that dumped 10-25 cm of snow just to the west, and east of Winnipeg.

I wish I had better news about warmer weather coming up..but long range models don't hint at anything normal or above normal until early May at the earliest. I looked longingly at those 30C+ temperatures today in southern Minnesota.. with a summerlike weekend heading into southern Ontario. I'm getting concerned that we're seeing a repeat of the spring of 1979, when we saw snow into the second week of May, and didn't see 20C temperatures until mid May! The optimist in me is saying that things gotta change sometime!

Latest GLB model shows Colorado low type system moving through northern Minnesota Sunday night into Monday with potential for significant snow over southeast MB and eastern ND. GFS model a little further south and east with this system, with bulk of snow missing southern MB. Will need to monitor to see how models trend with this one..

Looks like more of a rain event moving into southern MB Sunday afternoon..likely mixing with or changing to wet snow Sunday night. Bulk of pcpn expected mainly south and east of Winnipeg with 5-10 mm of rain and a couple cm of wet snow possible.. but I think Winnipeg will see some pcpn too.